DEVELOPMENT OF A REGIONAL CLIMATE MODEL OF THE WESTERN ARCTIC

An Arctic region climate system model has been developed to simulate c oupled interactions among the atmosphere, sea ice, ocean, and land sur face of the western Arctic. The atmospheric formulation is based upon the NCAR regional climate model RegCM2, and includes the NCAR Communit y Climate Model Version 2 radiation scheme and the Biosphere-Atmospher e Transfer Scheme. The dynamic-thermodynamic sea ice model includes th e Hibler-Flato cavitating fluid formulation and the Parkinson-Washingt on thermodynamic scheme linked to a mixed-layer ocean. Arctic winter a nd summer simulations have been performed at a 63 km resolution, drive n at the boundaries by analyses compiled at the European Centre for Me dium-Range Weather Forecasts. While the general spatial patterns are c onsistent with observations, the model shows biases when the results a re examined in detail. These biases appear to be consequences in part of the lack of parameterizations of ice dynamics and the ice phase in atmospheric moist processes in winter, but appear to have other causes in summer. The inclusion of sea ice dynamics has substantial impacts on the model results for winter. Locally, the fluxes of sensible and l atent heat increase by over 100 W m(-2) in regions where offshore wind s evacuate sea ice. Averaged over the entire domain, these effects res ult in root-mean-square differences of sensible heat flux and temperat ures of 15 W m(-2) and 2 degrees C. Other monthly simulations have add ressed the model sensitivity to the subgrid-scale moisture treatment, to ice-phase physics in the explicit moisture parameterization, and to changes in the relative humidity threshold for the autoconversion of cloud water to rainwater. The results suggest that the winter simulati on is most sensitive to the inclusion of ice phase physics, which resu lts in an increase of precipitation of approximately 50% and in a cool ing of several degrees over large portions of the domain. The summer s imulation shows little sensitivity to the ice phase and much stronger sensitivity to the convective parameterization, as expected.